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Gas Chromatography / Mass Spectrometry

Essential oils and absolutes are volatile which means that they have a tendency to vaporise. Analysis by gas chromatography produces a trace, which shows the order in which the constituents vaporise and the quantity of each constituent expressed as a percentage.

For example, cineol and terpinen-4-ol in tea tree will always show up in the same place on the time axis of the graph. The trace for good tea tree oil will always show a similar pattern.

Some oils have so many constituents (rose has over 400) that many of them do not even have names but are referred to simply by co-ordinates (time and  % quantity) on the trace. Many oils have constituents in common but the proportions differ which is why the have a different odour.

This form of analysis is routinely used in the industry in an attempt to remove subjectivity. The large users of essential oils want product repeatability so that their products are the same every year.

However, there are limitations to the technique.  Although a gas chromatography trace will tell us the quantity of each constituents, it cannot tell us whether the oil is pure or not. Supposing when tea tree oil is being distilled some eucalyptus is also put into the still; the resulting oil will be higher in cineol (quality eucalyptus is at least 80% cineol). An analysis by gas chromatography will tell us how much cineol is in the oil but it will not tell us that the source of some of the cineol was eucalyptus. Spanish rosemary may also be distilled with camphorwood to make a more economic oil.

Sticky substances (such as many pure absolutes and concretes) are not as volatile as oils and may clog up the equipment.  Many providers of GC / MS analysis are reluctant (or refuse) to analyse materials of this type.

The situation is made even more complex by the fact that so many of these constituents are available as natural isolates. It is an uncomfortable truth that if there were a reliable test for the purity of essential oils the market would not be flooded with cheap, low-quality adulterated oils.

We work closely with suppliers to ensure the quality of our oils, which may include examination of GC / MS traces.  But more than anything we strongly believe that the best approach to sourcing quality oils is by forming good relationships with trustworthy suppliers.